1. Field of the Invention
The present invention relates to an electron gun for a cathode ray tube (CRT), and more particularly, to an electrode having an improved structure and an electron gun using the same.
2. Description of the Related Art
In general, an electron gun for a color CRT is mounted within the neck portion of the CRT and emits electron beams for irradiating a fluorescent layer. As shown in FIG. 1, the electron gun includes a cathode structure 11, a control electrode 12 and a screen electrode 13 together constituting a triode section, and a plurality of focusing electrodes 14 constituting a main lens.
In the electron gun for a color CRT having the above-described configuration, as predetermined voltages are applied to the respective electrodes, electron beams emitted from an electron emitting material of the cathode structure 11 are focused and accelerated by electronic lenses formed among the respective electrodes and selectively deflected according to the scanning position of the fluorescent layer to then land on the fluorescent layer.
Such an electron gun for a color CRT is provided with static converging means and focusing means, for changing paths of three electron beams emitted from a cathode individually or wholly in the course of accelerating and focusing the electron beams, thereby achieving precision of convergence. However, the static convergence action of the electron beams is weakened by several causes including processing errors occurring while manufacturing the respective electrodes 11 through 14 constituting the electron gun, deformation of electrodes which is caused by an external force applied when fixing the electrodes in a bead glass, a shift in the positions of electron beam passing holes which is caused by thermal expansion of electrodes, and the like.
In particular, the triode section consisting of the cathode structure 11, the control electrode 12 adjacent thereto and the screen electrode 13, is subjected to heat treatment for heating an electron emitting material so that a thermal drift phenomenon of electron beams occurs due to thermal deformation, resulting in a convergence drift, and a cross-over point related to an objective point of an electron beam is formed. Thus, it is necessary to accurately control the size of an electron beam passing hole and the thickness of an electrode in the electron beam passing hole portion.
FIG. 2 illustrates an example of a plate-shaped electrode which functions as a control electrode or a screen electrode.
Referring to FIG. 2, an electrode 20 made of a single plate includes three electron beam passing holes RH, GH and BH formed on a plate-shaped main body 21 in an in-line arrangement, and depressions 22a, 22b and 22c which are disposed around the electron beam passing holes RH, GH and BH, for thinning the portions where the electron beam passing holes RH, GH and BH are formed. Also, beads 23a, 23b and 23c for reinforcing the strength of the electrode portions around the electron beam passing holes RH, GH and BH are formed around the depressions 22a, 22b and 22c. A plane portion 24 is disposed around the beads 23a, 23b and 23c, and supporting portions 25 which are embedded in a bead glass (not shown), for supporting the electrode 20, are formed at edges of the main body 21 along a lengthwise direction thereof. Also, assembly holes 26 for aligning the electron beam passing holes RH, GH and BH are provided at both sides of the main body 21 along the horizontal axis thereof.
Since the aforementioned electrode 20 for an electron gun has three electron beam passing holes RH, GH and BH formed in its main body 21 of a single plate in an in-line arrangement, it is very important to uniformly form pitches P and Pxe2x80x2 among the electron beam passing holes RH, GH and BH. The electron beam passing holes RH, GH and BH are formed by punching. In the case of forming the central electron beam passing hole and the side electron beam passing holes, the processing error in the pitch is xc2x10.005. That is, a high-precision processing technique is required for forming the electron beam passing holes within the error allowance.
Also, in the aforementioned electrode 20, the assembly holes 26 must maintain a difference of xc2x10.005 mm in the processing eccentricity. A difference in the thickness between the portions of the electron beam passing holes RH, GH and BH, which is caused by the depressions 22a, 22b and 22c, must be within the range of xc2x10.005 mm. However, as described above, since the single-plated electrode 20 is formed by a single mold, if a predetermined portion of the mold bears a difference beyond the allowance, the mold cannot function properly. Thus, maintenance of the predetermined portion is difficult to achieve, and the productivity is then lowered.
In the aforementioned conventional electrode 20, since the beads 23a, 23b and 23c and the depressions 22a, 22b and 22c are formed in an in-line arrangement in its main body 21 which is elongated horizontally, the areas of flat portions around the electron beam passing holes RH, GH and BH are not constant. In such a state, if the electrode 20 is heated at 980 to 1050xc2x0 C. for 8 to 10 minutes for the purpose of performing a hydrogen-reduction process for removing gases in the metal of the plate, the electrode 20 may be deformed due to asymmetrical processing stress and anisotropic shape stress.
In particular, since the plate-shaped electrode 20 is used as a control electrode installed to be adjacent to a cathode structure, the electrode 20 experiences thermal expansion due to heat generated from a heater of the cathode structure, as shown in FIG. 3. The thermal expansion shifts the positions of the electron beam passing holes RH, GH and BH formed in an in-line arrangement, relative to each other, to cause a thermal drift by which paths of the electron beams passing through the electron beam passing holes are shifted, which lowers the white-balancing characteristics and resolution of the CRT.
To solve the above problems, it is an object of the present invention to provide an electrode of an electron gun, which can improve precision of processing and productivity, and can prevent thermal drift of electron beams and improve focusing and white-balancing characteristics by preventing deformation of the electrode due to heat transfer from a heater of a cathode structure, and an electron gun for a cathode ray tube using the electrode.
It is another object of the present invention to provide an electrode of an electron gun including a first electrode member having supporting portions protruding from both edges thereof along a lengthwise direction, and three connection holes disposed in an in-line arrangement, and second electrode members connected to the connection holes of the first electrode member, and each having a plane portion where electron beam passing holes are formed, and a flange portion formed along the periphery of the plane portion and connected to the periphery of each connection hole of the first electrode member.
In the present invention, depressions are preferably formed by press-molding peripheries of the electron beam passing holes formed in the plane portion, and a bead is preferably formed between the plane portion and the flange portion.
Here, the shapes of the electron beam passing holes may be circular, elliptical or polygonal. Also, the weight of the central second electrode member may be different from that of either side second electrode member.
According to another aspect of the present invention, there is provided an electron gun for a cathode ray tube, the electron gun having a cathode, a control electrode and a screen electrode together constituting a triode section, and a plurality of focusing electrodes sequentially installed from the screen electrode, wherein the control electrode or the screen electrode includes a first electrode member having supporting portions protruding from both edges of the control electrode or the screen electrode along a lengthwise direction and having three connection holes disposed in an in-line arrangement, and second electrode members connected to the connection holes of the first electrode member, and each having a plane portion where electron beam passing holes are formed, and a flange portion formed along the periphery of the plane portion and connected to the periphery of each connection hole of the first electrode member.